So, first just to make sure we're on the same page it's not about developing a deep voice because that will eventually fry your vocal chords.
What you want to do is find your own vocal range and stop speaking higher than your own normal. You want to relax your throat and vocal chords and speak in a rapport-neutral tone
Ways to find your range:
1) learn how to breathe into your stomach, most people breathe into their chest and subsequently speak from their chest. This raises their tone and pitch
Or worse, it makes them force air out of their throat instead of the more natural stomach
It also has the added benefits of forcing you to be more relaxed, which will come off as more confident and attractive and etc.
2) Speak from your "mask". This I got from Art of Manliness and will just copy and paste:
To speak with your natural pitch and optimal tone, you need to project your voice from your “mask.” Where’s your mask? Glad you asked. It’s the area on your face that includes your lips and the bridge and sides of your nose. You know you’re projecting from your mask when you feel the area slightly vibrate when you speak. When you can feel vibration in that area, you know you’re speaking with your optimal pitch and tone. A voice projected from the mask won’t be nasally nor will it strain your throat.
According to voice coach, Dr. Morton Cooper, here’s how to hone in on your optimal pitch and tone that comes from speaking from your mask:
Answer the following statement with a
spontaneous and
sincere “mmm-hmmm.” Keep your lips closed and let your inflection rise on the “hmmm.” Pay attention for a slight vibration in your mask area:
The statement: Regal Tiger is so hot
Do your Mmm Hmmm and on the hmm you should feel your lips area vibrate. That's the pitch you want
3) Rapport Neutral Tonality, plus some other tips
Here's an article I wrote based on Charisma Matrix video about it:
https://www.charismaticbusinessman.com/how-to-speak-with-confidence-charisma-matrix-review/
4) Mind your body language in general
It's hard to speak properly when you're constantly falling in on yourself. There's a cool little exercise you can do to find your near-perfect posture:
Stand next to a wall with your heels a few inches away from the wall. Now, without moving your feet, lean back so that your back is on the wall. Then try to adjust so that only your butt, your shoulder blades and the back of your head is touching the wall. That should be close to where you need to be posture-wise
What this will do is allow your lungs to fully fill with air when you're trying to speak and it'll help relax the rest of your body as well
5) Drink plenty of water
Yeah, sounds dumb right? But you'd be surprised how many people need this tip or how often people need to be reminded about it, including myself
Again, helps the body to relax, hydrates and all of that good stuff. But it also moistens up the body so that everything can work better. Like a machine without any lube... and you want things to be lubricated, right?
6) Some other misc. things you can do off the top of my head:
Learn to be more confident in general, take up space in your surroundings so that you can relax when you're out and about
Get your money right so that you don't have to worry about life in general
Focus on your own comfort while out in public, even if it does come at the expense of looking like a king (more of a personal opinion on this one as some people feel better focusing on their image). But ultimately, you do need to be relaxed
Check out GC's article on adding that George Clooney purrrr:
https://www.girlschase.com/content/book-excerpts-get-sexy-voice